Blogging is something that requires patience, persistence and discipline. It may mean writing everyday for over a year before you really start to see any money from it. There are exceptions to the rule, but from my dealings with other bloggers, it seems to be pretty common to spend one or even two years building your blog, your brand and your authority, before making any serious amount of money.
Coding – whether for developing apps or designing websites – is another big business online! It’s a pretty egalitarian business as well, since you can teach yourself to code in many languages and you can code from wherever you are. At its most basic, all you need is a computer (or laptop or tablet), an Internet connection for connecting with project files or far-flung colleagues, and a text editor. (The software involved can get more complicated than that, as you go along.) There are more small businesses wanting customized websites and startups trying to create that next great app every day, and coders can make a living along the way.
The topic you choose must have enough depth that you can create a lot of content for it. This is important for building an authoritative site, for search engine optimization, and most importantly, for the end user. If you don't have enough content about a topic, you're not going to be taken very seriously as an authority on the topic and it's unlikely you can convince someone to make a purchase from you.